Light-stable sheet material for recording light-images

ABSTRACT

Sheet material which initially is unaffected by exposure to light is rendered light-sensitive upon brief heating and thereafter upon being exposed to a light-image followed by further limited heating will develop a visible image.

United States Patent 1191 [11] 3,802,888 Willits Apr. 9, 1974 [54] LIGHT-STABLE SHEET MATERIAL FOR 3.635.719 1/1972 Ohkubo et a1. 96/1 14.1 RECORDING UGHTJMAGES 3,645,739 2/1972 Ohkubo e! 111 7 96/1141 3,707,377 12/1972 Tiers ct a1 117/3611 Inventor: J y s, mt ul, lnn. 2,929,736 3/1966 Miller et a1. 117/3619 Assignee: Minnesota Mining and 3,589,903 6/1971 Blrkelzmd 96/67 Manufacturing Company, St. Paul, Minfl- Primary Examiner-J. Travis Brown Assistant E.\'aminer-Richard L. Schilling 7 [22] Filed Oct l9 1 Attorney, Agent, or Firm-Alexander, Sell, Steldt & [21 Appl. No.: 191,803 Delahunt [52] US. Cl 96/ll4.l, 96/67, 96/94 R,

117/368, 117/369 [57] ABSTRACT 51 Int. Cl. 603C 1/72, G036 1/76, 603C 1/02,

341m 5 /00 Sheet matenal wh1ch 1n1t1ally 1s unaffected by expo- 58 Field of Search 96/1 14.1, 67, 94 R; Sure to light is rendered light-Sensitive upon brief heal- I 1 17/368 36.9; 250/65 T ing and thereafter upon being exposed to a light-image followed by further limited heating will develop a visi- {56} References Cited ble image- UNITED STATES PATENTS 4 Claims, No Drawings $756,829 9/1973 Ohkubo et a1, 96/114.1

1 LIGHT-STABLE SHEET MATERIAL FOR RECORDING LIGHT-IMAGES This invention relates to the recording of lightimages, with particular reference to novel sheet materials for use therein. There is provided an initially substantially light-insensitive or light-stable sheet material which is rendered highly light-sensitive upon mere heating and which thereafter when first exposed to a light-image will develop a visible image under further restricted heating. Thus the sheet material may initially be manufactured, packed, and manipulated while exposed to light, and may thereafter, on demand, be quickly and easily made light-sensitive by simple heating. Sensitization may be accomplished by heating the entire sheet; alternatively, small segments of the lightstable sheet may independently be sensitized, exposed and developed. The product is therefore particularly useful in the form of microfiche cards adapted for the cumulative recording of intelligence.

US. Pat. No. 3,589,903, the disclosures whereof are by reference incorporated herein, describes the preparation of a light-sensitive heat-developable sheet material by converting to photosensitive silver halide a small proportion of the silver content of a single or multiple layer coating or stratum containing an organic silver salt oxidizing agent, a reducing agent, and mercury ion. The last-named component is conveniently introduced in the form of mercuric bromide, the bromide ion then promptly reacting with the silver salt to provide the required photosensitive silver halide. Other sources of halide ion may be used, and other components including binders, toners, spectral sensitizers, preservatives, inert fillers, etc., may be included.

The present invention may and frequently does employ similar components and similar proportions but uses critically different procedures resulting in latent rather than immediate light-sensitivity.

The procedures employed serve to maintain the silver salt and the source of halide ion in interreactive proximity so as substantially to prevent any initial photosensitivity but so that, upon subsequent appropriate manipulation primarily involving the application of heat, interreaction occurs with formation of photosensitive silver halide in full catalytic proximity with the remaining organic silver salt.

In one form of the invention the organic silver salt and the source of halide ion are laid down'in separate layers with an intervening separate thin layer of a'suitable film-forming thermoplastic binder. Preferably, however, the binder is incorporated with the silver salt and is of a specific type and in sufficient quantity to protect the salt from reaction with the halide until such time as the stratum is heated. For this purpose the polyvinyl acetal resins, such as polyvinyl butyral and polyvinyl formal, are found to be particularly effective. Yet even these preferred materials must be employed with suitable precautions in order to avoid premature reaction between silver salt and halide ion. Thus it is necessary that the silver salt be protected with the binder prior to introduction of the halide. Separation and avoidance of premature reaction of silver salt and halide may be achieve by coating in two layers, the first being dried prior to application of the second, the volatile vehicle of the second being preferably a nonsolvent for the dried first layer or at least being removed promptly so as to avoid any substantial contact produce a coated sheet showing no evidence of photosensitivity; whereas the same composition when first permitted to stand for as little as two to five hours prior to coating, or when inhibited from prompt evaporation of solvent after coating, is found to yield an obviously light-sensitive sheet.

Plasticizing of the polyvinyl acetal binder likewise has a tendency to permit migration and premature reaction of silver soap and halide; thus silver behenate half soap, a mixture of equimolar amounts of silver behenate and behenic acid, has been found ineffective in 7 sheets where prolonged stability is required, apparently due to the plasticizing effect of the free behenic acid.

As in US Pat. No. 3,589,903, mercuric halide may be used as the sole source of halide ion; but the necessary amount of halide ion is preferably here obtained in whole or in part from some other source. Chlorides, bromides and iodides of calcium, nickel or cobalt are illustrative of other sources of halide ion which may be used. The halide ions of these several compounds may be titrated with alcoholic silver nitrate solution and are found to be readily reactive with the organic silver soap.

As previously noted, the invention makes possible a microfiche card or transparency which may be handled under room light or used in appropriate viewing or pro- 40 jection apparatus without damage. When graphic intelligence is to be imparted to an initial or added small area of the card, the area is quickly and conveniently sensitized by brief heating, whereupon the desired image is imparted by exposure to a light-image followed by heat development, the remaining unheated areas of the card remaining non-light-sensitive.

The practice of the invention will now be further described by means of illustrative but non-limiting Examples.

EXAMPLE 1 Silver behenate, prepared by precipitation with silver nitrate from an equimolar proportion of the sodium salt of commercial behenic acid, is well dispersed in a mixture of toluene and methylethyl ketone by multiple passes through a homogenizer to form a thick slurry containing 20 weight percent of the silver soap. A coating composition containing grams of methyl isobutyl ketone, and 20 ml. of a solution of 0.5 gram spectral sensitizing dye (RF-341) in 1,000 ml. of methanol, is coated on heat-resistant thin transparent polyethylene glycol terephthalate polyester film using a coating orifice of four mils. The coating is dried. A second coating, of a solution of 15 parts by weight of Vinylite VYLF ketone-soluble vinyl chloride-vinyl acetate copolymer in 100 parts of acetone, is applied at an orifice of 2 mils and allowed to dry. A third coating, also at an orifice of 2 mils, is then applied and permitted to dry at room temperature; it contains, in parts by weight:

phthalazinone All operations are performed under normal room light- Nonox WSO is a hindered phenol identified as l, l bis(2-hydroxy-3,S-dimethylphenyD-B,5,5- trimethylhexane.

Spectral sensitizers include merocyanine sensitizing dyes, such for example as 3-allyl-5-(3-ethyi-(2- naphthoxazoylidene)ethylidene)-l-pheny1-2- thiohydantoin.

The coated film is held for several seconds in contact with a platen maintained at 250 F., with no visible change. It is then exposed for 15 seconds to a light-image from a projection lamp, and reheated. A visible image develops within about ten seconds.

When heated at substantially higher temperatures, the sheet will darken uniformly due to a relatively slow oxidation-reduction reaction between the silver soap intensity of about 200 foot-candles, and heated by contact with a 250 F. platen for several seconds. Samples which remain unchanged in appearance after such treatment are next exposed to a light-image at the same intensity for 5 seconds and again heated at 250 F. for a time just sufficient to develop maximum darkening at image areas while avoiding as far as possible any significant darkening at the unexposed background areas. Further samples of the doubly coated film segments prior to initial heating are exposed to normal room light for two hours before being heated, exposed to a light-image, and heat-developed; and the test is repeated with a third set of samples, with preliminary exposure continued for 16 hours. Image and background areas of all pertinent specimens are measured for diffuse transmission optical density using the MacBeth Quantalog densitometer and the results are expressed as maximum (D max) and minimum (D min) densities respectively.

The maximum measurable density is 4 and the notation 4/4 therefore indicates that the entire sheet has been fully sensitized under the indicated pre-exposure. Of the formulas tested, it is apparent that maximum contrast and maximum stability are achieved in composition E employing a mixture of mercuric bromide and calcium bromide as the source of halide ion.

Segment A B C D E F G Salt added Amount, grams AlBr .12 .05 .l2 .25 HgBr .05 .05 .l .05 .05 .05 i2 CaBr- .i

NH,Br M 1 Prc'exposurc unn/ u.

sec. .l2 .12 .l2 I2 .16 .l6 .l2

200 ofc T5Z l fh A iii 3i 1 Z l.l 7 .37 Zhrs. room .lfi .38 .15 4 .l2 4 .12

1.1 l .67 2. l 3 4 4 4 .28 16 hrs. room 4 4 .19 .24 4

and the hindered phenol. The reaction is catalytically EXAMPLE 3 accelerated at the exposed areas of the sensitized coating. Application of heat during development is controlled to obtain maximum image density consistent with minimum backgrounding.

EXAMPLE 2 A first coating composition is prepared by adding grams of polyvinyl butyral (Butvar B 76") resin to a homogenatedye mixture prepared as in Example 1, with agitation in a high speed mixer. The resulting smooth liquid is coated on 5 mil transparent polyester film using a 5 mil orifice and allowed to dry.

Segments of the coated film are separately further coated at 3 mils with compositions each containing grams of a master batch prepared by mixing together 10 grams of cellulose acetate butyrate, 100 grams of methanol, 2 grams of phthalazinone, and a solution of 6 grams of hindered phenol (Nonox WSO) in 50 ml. of acetone, together with one or more halogencontaining salts as hereinafter tabulated, the salts being first dissolved in a small quantity of methanol for ease in mixing. The doubly coated film segments are allowed to dry at room temperature. They are first exposed for 15 seconds to light from a projection apparatus at an in a further test of variations on segment E of the preceding Example, quantity of mercuric bromide is varied from 0.05 to 0.15 gram and of calcium bromide from 0.2 to 0.4 gram, best results in terms of maximum contrast and stability being attained at 0.05 gram of the mercury salt and 0.35 gram of the calcium salt. This last-defined sheet is further tested to determine optimum time-temperature conditions for photosensitizing Time of heating (sec.) Temp. "F D,

At sensitization temperatures of F. to 210 F. and times of 2 to 20 seconds the density obtained on subsequent exposure and heat development is in the 0.05 0.10 range.

In another test to determine optimum exposure time, a sheet prepared as above described but using 0.05 gram mercuric bromide and 0.03 gram of calcium bromide is first sensitized by brief heating at 245 F. under darkroom conditions, exposed to light from a UV sensitometer at separate areas for different times, and devel oped by heating for 5 seconds at 245? F. The image density is then measured. Maximum density is attained under these conditions with exposure of 25 seconds and the density is maintained at substantially the same level as time of exposure is increased to a maximum of 4 minutes. Under the same exposure and development conditions the unsensitized sheet shows a constant density of 0.05.

The reaction between the halide salt and the silver salt to produce photosensitive silver halide is inhibited in Example 1 by the intervening film of vinyl chloridevinyl acetate copolymer, and much more effectively in Examples 2and 3 by the presence of the polyvinyl acetal resin. The effect of variations in the proportions of this last-named material will now be further described.

EXAMPLE 4 A mixture of 13 parts by weight of silver behenate in 87 parts of mixed toluene and methylethyl ketone is homogenized and to each 100 grams of homogenate is added one ml. of sensitizer solution as defined in Example 1. Polyvinyl butyral resin is then added in different amounts to portions of the mixture and the well mixed compositions are separately coated at a thickness of 4 mils on polyester film, dried and overcoated at 3 mils with a composition containing 2 grams phthalazinone, 6 grams Nonox WSO reducing agent, and 1.4 ml. of a 10% solution of mercuric bromide in methanol, all dissolved in a mixture of 100 grams of acetone and 30 grams of methanol. The coatings are dried at room temperature. Each segment is divided into two portions. One portion of each is exposed to light and is then heated at 260 F. to incipient backgrounding. The other portion is first heated at 260 F. for two seconds and is then exposed to light and again heated. Density measurements are made on all portions, with the following results:

gm. resin/gm.

Ag. soap .15 .30 .45 .60 .75 .85 .95 1.2 pr iieated 3.3 3.8 4 3.9 4 3.9 4 3.9 D not preheated 3.3 3.8 4 2.8 2 0.2 0.05 .05

EXAMPLE 5 A mixture of parts by weight of silver behenate in 85 parts of a 1:1 mixture of toluene and methylethyl ketone is homogenized to form a thick paste. To 17 parts by weight of the homogenate is added 35 parts of a 35% solution of polyvinyl butyral resin in methylethyl ketone with intensive mixing, resulting in -a milky liquid.

To this material is then added 0.25 part of phthalazinone, 0.1 part of mercuric bromide, and 0.8 part of a hindered phenol, in this instance bis( 2-hydroxy-3,5- ditertiarybutylphenyl) methane. The well stirred mixture is promptly coated on 3 mil transparent polyester film using a coating blade at an orifice of 3 mils and the coating is promptly dried. A protective coating of two mils of a 5% solution of cellulose acetate in acetone is applied over the silver-containing coating and the product is again promptly dried under forced ventilation at room temperature.

A portion of the coated film is first exposed to a lightimage at approximately 10 foot-candle-seconds from a tungsten filament source, and is then heated for 10 seconds at 138 C. No visible change is apparent, the optical density remaining at about 0.1.

Another portion of the film is first held for 15 seconds in contact with a metal block maintained at C. It is then exposed through a step wedge to tungsten radiation followed by heating for 10 seconds at 138 C resulting in a visible image having an optical density of 1.0 in the area exposed at 5 X 10 foot-candle-seconds.

The film may alternatively be rendered photosensitive by the action of a volatile solvent. As an example, acetone is applied to the surface of the film while exposed to light, and is permitted to dry slowly. The film is then heated. The solvent-treated area is darkened; the remaining areas remain unchanged.

What is claimed is as follows:

1. Sheet material which after being exposed to normal indoor illumination for several hours and then heated for a few seconds at a photosensitizing temperature within the range 2 10- 285 F. remains visibly substantially unaltered but which when first thus heated and then exposed image-wise to said illumination for not more than a few minutes and then again heated undergoes substantial darkening at the light-struck image areas; said sheet material including a stratum containing an organic silver salt oxidizing agent, a hindered phenol reducing agent for silver ion, a source of mercury ions in significant small amount up to about 0.07 mol of mercury per mol of silver, and a source of halide ion in significant small amount equivalent to not more than about fifteen molar percent based on the amount of said silver salt, and wherein said silver salt and said source of. halide ion are held in closely spaced interreactive proximity by an intervening thermoplastic film-forming binder.

2. Sheet material according to claim 1 wherein said binder is a polyvinyl acetal resin.

3. Sheet material according to claim 1 wherein said binder is polyvinyl butyral and said stratum contains phthalazinone.

4. Sheet material according to claim 3 wherein said binder is present to the extent by weight of at least about three-fourths the weight of the organic silver salt. 1

UNITED STATES PATENT OFFICE CERTIFIQATE 0F CORRECTION Patent N0. 3 8 Q2 ggg Dated -11 9, 197 4 Inventor(s) Jerry G Willibs t is certifiedthat error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 8, for "for" substitute For Column 2, line 58 after "100 grams of", insert the homogenate, 100 grams of Column 3, line 53, insert the hyphen in "homogenate-dye".

Column l, Table 1, lower portion of table, rewrite to read as follows:

Pre-exposure Dmin. Dmax.

15 sec 200 0 .12 .12 .12 .12 .16 .16 .12 2.55 1.35 2.58 4 H 1.17 i .37 2 hrs. room .16 8 .15 4 .12 u .12 1.11 7 2.13 f T .2'8 16 hrs. room 8 4 .19 .2 4 l Signed and sealed this 1st day of October 1974.

; (SEAL) 5 Attest:

I MCCOY M. GIBSON JR. c. MARSHALL DANN i Attesting Officer Commissioner of Patents UscOMM-DC 60378-PO9 rus caveman; nmmuc. arncc nu o-nu-n: 

2. Sheet material according to claim 1 wherein said binder is a polyvinyl acetal resin.
 3. Sheet material according to claim 1 wherein said binder is polyvinyl butyral and said stratum contains phthalazinone.
 4. Sheet material according to claim 3 wherein said binder is present to the extent by weight of at least about three-fourths the weight of the organic silver salt. 